4000CS Quattro cuts out when warm

Like the title says, the car will kill and won't start until it cools down to ambient. It seems the cooler it is outside the less likely the car is to kill. The car doesn't misfire it just flat out dies. Sometimes it can be brought back to life by down shifting into a lower gear and bringing up the RPM. I don't get it... otherwise it runs just fine.

Any insight would be great.